Corrosion inhibitor composition applicable for aluminum and steel  protection and procedure

ABSTRACT

A corrosion-inhibiting composition for application to a metal substrate, such as aluminum or steel, and in connection with a paint, and the synthesis of the composition. The active inhibitor constituent of the composition can be selected from the group consisting of 2,5-dimercapto-1,3,4 thiadiazole (DMTD), 2,4-dimercapto-s-triazolo-[4,3-b]-1,3-4-thiadiazole, trithiocyanuric acid (TMT), and derivatives of DMTD and TMT, including various N— or S— and N, N—, S— and N—,S-substituted derivatives of DMTD, including salts of DMTD of the general formula: M(DMTD) n , where n=1,2 or 3, and M is a metal cation and preferably M=Zn(II), Bi(III), Co(II), Ni(II), Cd(II), Pb(II), Ag(I), Sb(III), Cu(II), Li(I), Ca(II), Sr(II), Mg(II), La(III), Ce(III), Pr(III), Al(III) or Zr(IV). DMTD, TMT, and their derivatives may also be combined with phosphates, molybdates, borates, silicates, tungstates, phosphotungstates, phosphomolybdates, cyanamides, carbonates, SiO 2  and mixtures thereof.

RELATED APPLICATION

This application is a continuation-in-part application of applicationSer. No. 10/138,794, filed 3 May 2002 now abandoned, which claims thebenefit of provisional application Ser. No. 60/288,895, filed 4 May2001.

BACKGROUND OF THE INVENTION

Protection of aluminum against atmospheric corrosion constitutes achallenge of significant economic importance. Several distinct aluminumalloys are known, characterized by different susceptibility toatmospheric corrosion. Among others, aluminum alloys containing a smallpercentage of Cu are well known and valued for their excellentmechanical properties, as, for example, Al 2024 T-3, widely applied inaircraft manufacturing industry.

It is well known, however, that due to copper rich intermetallic speciesrandomly distributed in the aluminum matrix, which are spontaneouslypolarized as cathodic sites and catalyze the O₂ reduction, the cathodicreaction of atmospheric corrosion, Al 2024 T-3 is also more susceptibleto atmospheric corrosion.

There are two distinct corrosion control technologies commonly appliedto protect aluminum alloys (such as Al 2024 T-3) against atmosphericcorrosion: conversion coatings and organic coatings.

As for conversion coatings, Alodine 1200 is one of the well-knowncorrosion inhibitor technology widely applied for Al 2024 T-3protection. It is based on soluble chromates containing CrO₄ ⁻⁻ as aninhibitor species and yields a robust conversion coating on aluminumsubstrates. A measure of its robustness, Alodine 1200 conversion coatingon Al 2024 T-3 aluminum panels is known to resist salt spray exposure inexcess of 300 hours, without pitting. In addition, conversion coatingsare designed to enhance the adhesion of organic primers subsequentlyapplied on aluminum substrates, a requirement also satisfied by Alodine1200. Such procedures using chromates are thus considered to be thestandard of the industry with respect to obtainable protectionperformance.

Aircraft primers and coil primers are the typical high performanceorganic coatings that are applied for protection of aluminum, such asespecially in the aircraft manufacturing industry. A thickness of lessthan 20 micron is characteristic of these primers, which thus provide anegligible barrier function and, consequently, mandate the use ofeffective corrosion inhibitor pigments.

As is well known, pigment grade corrosion inhibitors used in organicprimers must contain anionic species with inhibitor activity and must becharacterized by limited, but effective, solubility in water. For thesereasons, it will be apparent that CrO₄ ⁻⁻ is the corrosion inhibitorspecies preferred in both corrosion control technologies applied onaluminum for protection against atmospheric corrosion that is inconversion coatings and high performance organic primers.

SrCrO₄ is the corrosion inhibitor pigment of choice for aircraft andcoil primers, and is the standard in the industry. Due to environmentalconcerns, finding a replacement for chromates in conversion coatings andorganic coatings constitutes the objective of contemporary research inthis field.

It is generally known that if toxicity, efficiency, and price areconsidered, the number of inorganic corrosion inhibitor speciesavailable for chromate replacement is limited essentially to a fewanionic species, and specifically to MoO₄ ⁻⁻, PO₄ ⁻⁻, BO₂ ⁻⁻, SiO₄ ⁻⁻and NCN⁻. As a consequence, all commercial non-chromate corrosioninhibitor pigments are molybdates, phosphates, borates, silicates orcyanamides, or combinations of these compounds. Except for Zn-(II) andCe, which are credited with some degree of efficiency, the directcontribution of cationic species to the corrosion inhibitor performanceof pigments is marginal. However, cations do determine the solubilityand hydrolysis pH of pigments.

In comparison to CrO₄ ⁻⁻, inherent limitations of their corrosionpreventing mechanism render these above-specified anionic species lesseffective inhibitors of corrosion, in general, and specifically ofatmospheric corrosion of aluminum. Consequently, it appears thatinorganic chemistry is unable to produce inhibitors of atmosphericcorrosion, which could be comparably effective, non-toxic alternative ofCrO₄ ⁻⁻. In contrast, a large arsenal of organic corrosion inhibitor isknown and applied in various corrosion control technologies. Excessivesolubility in water and/or volatility of most of the known organicinhibitors appear to be the physical properties that are inconsistentwith applications in conversion coating technologies and in organiccoatings. To date, no organic corrosion inhibitor is known to be aneffective replacement of chromates in conversion coatings or organiccoatings intended for metal protection.

SUMMARY OF THE INVENTION

It has been discovered pursuant to the present invention that organiccompounds possessing cyclic structural features of aromatic character,carbocyclic and, specifically, heterocyclic aromatic structurescontaining one or multiple hetero species, such as, specifically, N, S,O atoms or combinations of the same, and preferably multiple —SH(mercapto) and ═S, or thiol-thion functionalities attached, areeffective inhibitors of corrosion of aluminum and its alloys. Thisdiscovery was not anticipated, considering that thiol-organic compounds(or/and H₂S) do not form essentially insoluble compounds (salts) with Al(III). As known, forming essentially insoluble (in water) compounds withionic species of a specific metal is a general prerequisite forcorrosion inhibitor activity of organic compounds on the respectivemetal substrate.

Specifically, the family of thio-organic compounds that includesdi-mercapto and poly-mercapto compounds and their derivatives has beenestablished as effective corrosion inhibiting products.

The following di- or poly-mercapto organic compounds are applicable:

di-mercapto derivatives of thiophene, pyrrole, furane, and of diazolesand thiadiazoles;

di- and tri-mercapto derivatives of pyridine, diazines, triazines and ofbenzimidazole and benzthiazole;

The following compounds and related derivatives are specificallyidentified:

2,5-dimercapto-1,3,4-thiadiazole or Bismuthiol 1 and2,4-dimercapto-s-triazolo-[4,3-b]-1,3-4-thiadiazole or C₃H₂N₄S₃, and5,5′-dithiobis(1,3,4-thiadiazole-2(3H)-thione and5,5′-thiobis(1,3,4-thiadiazole-2(3H)-thione; and

1,3,5-triazine-2,4,6(1H,3H,5H)-trithione, or trithiocyanuric acid (TMT),and dithiocyanuric acid,

dimercaptopyridine, 2,4-dithiohydantoine, and2,4-dimercapto-6-amino-5-triazine.

Applicable derivatives of the above-specified di- and poly-mercaptoorganic compounds include:

-   -   salts formed with metal cationic species,    -   alkyl-, aryl- and quaternary-ammonium salts,    -   various N- and S-substituted derivatives, such as        5-mercapto-3-phenyl-1,3,4-thiadiazoline-2-thione or Bismuthiol        II;    -   various N,N-, S,S- and N,S-substituted derivatives of the above        compounds; and    -   dimer and polymer derivatives of the above, resulted form        oxidative dimerization or polymerization of di- and        poly-mercapto compounds.

More specifically, it has been discovered that 2,5-dimercapto-1,3,4thiadiazole symbolized by HS—CN₂SC—SH or “DMTD” and its derivativesinhibit atmospheric corrosion of aluminum, including Al 2024 T-3. It hasbeen also proven that DMTD and various DMTD derivatives in pigment gradeform are applicable as components of organic primers or in soluble orpartially soluble form as an inhibitor constituent of conversion coatingcompositions intended for aluminum protection.

This discovery was unexpected, considering that DMTD does not formessentially insoluble compounds with Al(III), of which thischaracteristic is generally a prerequisite for corrosion inhibitionactivity of organic compounds on metal substrates.

Although unexpected, this effect is explicable in light of the presentresearch, however, considering the high chemical affinity displayed byorganic thiol derivatives, in general, and specifically by DMTD and TMT,toward Cu(II) and Cu-rich surfaces. In the specific case of DMTD, it hasbeen shown that DMTD spontaneously forms stable chemisorbtion layers oncathodically polarized Cu surface and, consequently, inhibits cathodicO₂ reduction in aqueous conditions. Based on this, it can be reasonableassumed that DMTD operates by similar mechanism on (cathodic) Cu-richintermetallics of Al-2024 in atmospheric conditions.

Along with DMTD, it has also been discovered pursuant to the presentinvention, that trithiocyanuric acid, or TMT, which can be classified asa tri-mercapto derivative, and its derivatives are also effectivecorrosion inhibitors of aluminum in a similar fashion as DMTD. It hasalso been discovered that DMTD and TMT and their derivatives areeffective corrosion inhibitors of galvanized steel and similar metalsubstrates, where these compounds interact with and protect thesacrificial zinc layer and, thus, indirectly protect the steelsubstrate.

More specifically, while Zn(II)-DMTD salts have been previouslymentioned in Sinko's U.S. Pat. No. 6,139,610, assigned to the sameassignee as the present invention, other metal DMTD and TMT salts havebeen synthesized pursuant to the present invention and determined to beeffective corrosion inhibitors, such as: Bi(III), Co(II), Cd(II),Pb(II), Ag(I), Sb(III), Sn(II), Cu(II), Fe(II), Ni(II) and also thecomparable soluble Li(I), Ca(II), Sr(II), Mg(II), La(III), Ce(III),Pr(III), Zr(IV) salts.

Furthermore, it has been determined pursuant to the present inventionthat inherently conductive polymers, such as polyaniline, polythiophene,polypyrrole, if protonated (i.e. doped) with mercapto-derivatives ofacidic character and specifically with DMTD, TMT and relatedderivatives, are useful as corrosion inhibitors. It will be apparentthat these resultant compounds formally are regarded as salts of DMTDand TMT formed with conductive polymers.

BRIEF DESCRIPTION OF THE DRAWING

FIGS. 1-13 are graphical prints representing IR spectra of productsproduced pursuant to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The following description will describe in detail the synthesis ofselected derivatives of 2,5-dimercapto-1,3,4 thiadiazole symbolized byHS—CN₂SC—SH or “DMTD”, and of selected derivatives of trythiocyanuricacid, or “TMT”, preferably used for application as a corrosion inhibitorin connection with a paint. DMTD, which is a di-mercapto derivative, andTMT, which is a tri-mercapto derivative, generally may be classifiedtogether. While it is believed that these corrosion inhibitors areapplicable to a wide range of substrates, the following descriptionreveals examples of applications to aluminum, galvanized steel, andsimilar metal substrates.

The following are examples of DMTD, TMT, and derivatives of DMTD and TMTapplicable to the practice of the invention:

1. 2,5-dimercapto-1,3,4 thiadiazole (DMTD), and2,4-dimercapto-s-triazolo-[4,3-b]-1,3-4-thiadiazole, and trithiocyanuricacid (TMT);

2. Various N-,S- and N,N-, S,S- and N,S-substituted derivatives of DMTDsuch as 5-mercapto-3-phenil-1,3,4-thiadiazoline-2-thione or bismuthiolII; various S-substituted derivatives of trithiocyanuric acid;

3. 5,5′ dithio-bis (1,3,4 thiadiazole-2(3H)-thione or (DMTD)₂, or(DMTD), the polymer of DMTD; 5,5′ thio-bis (1,3,4thiadiazole-2(3H)-thione; (TMT)₂, the dimer and polymers of TMT;

4. Salts of DMTD of the general formula: M(DMTD)_(n), where n=1, 2 or 3,and M is a metal cation and preferable M=Zn(II), Bi(III), Co(II),Ni(II), Cd(II), Pb(II), Ag(I), Sb(III), Sn(II), Fe(II), or Cu(II)(examples: ZnDMTD, Zn(DMTD)₂, Bi(DMTD)₃); similar salts of TMT, as forexample, ZnTMT, in a ratio of 1:1; and, also, the comparable solubleLi(I), Ca(II), Sr(II), Mg(II), La(III), Ce(III), Pr(III), Zr(IV) salts

5. Salts of (DMTD)_(n) of general formula M[(DMTD)_(n)]_(m), where n=2or n>2, m=1, 2, or 3 and M is as above specified in 4. Typical examplesare: Zn[(DMTD)₂], Zn[(DMTD)₂]₂;

6. Ammonium-, aryl-, or alkyl-ammonium salts of DMTD, (DMTD)_(n), or5,5′ thio-bis (1,3,4 thiadiazole-2(3H)-thione or2,4-dimercapto-s-triazolo-[4,3-b]-1,3-4-thiadiazole. Typical examplesinclude: Cyclohexyl amine: DMTD, in ratios of 1:1 and 2:1; Di-cyclohexylamine: DMTD, in ratios of 1:1 and 2:1; Aniline: DMTD, in ratios of 1:1and 2:1; similar salts of TMT, as for example Di-cyclohexyl amine: TMT,in a ratio of 1:1;

7. Quaternary ammonium salts of DMTD or (DMTD)_(n), and TMT

8. Poly-ammonium salt of DMTD or (DMTD)_(n) and TMT formed withpolyamines;

9. Inherently conductive polyaniline doped with DMTD or (DMTD)₂ or5,5′thio-bis (1,3,4 thiadiazole-2(3H)-thione and TMT

10. Inherently conductive polypyrrol and/or polythiophen doped withDMTD, (DMTD)₂ and 5,5′ thio-bis (1,3,4 thiadiazole-2(3H)-thione and/orTMT;

11. Micro or nano composites of poly DMTD/polyaniline, polyDMTD/polypyrrol, and poly DMTD/polythiophen; similar micro or nanocomposites with TMT; and with 5,5′ thio-bis (1,3,4thiadiazole-2(3H)-thione; DMTD or salts of DMTD or derivatives of DMTDand of TMT, as organic constituents of various pigment grade inorganicmatrixes or physical mixtures; it will be apparent that, with no intentto limit the concept of the present invention, such inorganic matrixesare preferable constituted of non-toxic anionic and cationic specieswith corrosion inhibitor properties, such as: MoO₄ ⁻⁻, PO₄ ⁻⁻, HPO₃ ⁻⁻,poly-phosphates, BO₂ ⁻⁻, SiO₄ ⁻⁻, NCN⁻, WO₄ ⁻⁻, phosphomolybdate,phosphotungstate and respectively, Mg, Ca, Sr, La, Ce, Zn, Fe, Al, Bi.

12. DMTD or salts of DMTD or derivatives of DMTD and TMT in encapsulatedforms, such as: inclusions in various polymer matrices, or ascyclodextrin-inclusion compounds or in microencapsulated form; and

13. various combinations of all of the above. Likewise, it is understoodthat the above list is not conclusive, and similar compounds andderivatives will yield similar results.

Pigment grade forms of DMTD include Zn(DMTD)₂ and Zn-DMTD (among otherorganic and inorganic salts of the former) and combinations of thelatter with inorganic products or corrosion inhibitor pigments, such as:phosphates, molybdates, borates, silicates, tungstates,phosphotungstates, phosphomolybdates, cyanamides or carbonates of thepreviously specified cationic species, as well as selected oxides.Examples include: zinc phosphate, cerium molybdate, calcium silicate,strontium borate, zinc cyanamide, cerium phosphotungstate andrespectively, ZnO, CeO₂, ZrO₂ amorphous SiO₂ or combinations of thesecompounds;

Regarding the synthesis of the Zn salts of DMTD, it has been discoveredpursuant to the present invention, that the spontaneous reaction of ZnOand DMTD yields exclusively Zn(DMTD)₂, as follows:ZnO+2HS—CN₂SC—SH═Zn(—S—CN₂SC—SH)₂+H₂O   1

Reaction 1 implies that, apparently, Zn-DMTD cannot be produced bysimply adjusting the DMTD/ZnO stoichiometric ratio to 1:1.

Di-mercapto derivatives useful in the practice of the invention arethose having a limited solubility in water, from about 0.01 and 1000millimoles (mmole) per liter. The greatly preferred range ofsolubilities is 0.1 to 10 mmole/l.

EXAMPLES Example 1

This example is intended to disclose the synthesis of Zn(DMTD)₂according to the above-presented Reaction 1.

As known, DMTD forms two distinct Zn(II) salts; that is, Zn-DMTD or the1:1 salts, and Zn(DMTD)₂ or the 1:2 salts. Each compound can beconveniently prepared by double decomposition in an aqueous medium,using, in corresponding stoichiometrical ratio, soluble Zn(II) salts andsoluble salts of DMTD, such as Na₂-DMTD and Na-DMTD, respectively.Intuitively, both salts are also expected to form by reacting ZnO andDMTD, in a 1:1 or 1:2 stoichiometrical ratio, respectively.

It has been discovered pursuant to the present invention, however, thatby reacting ZnO and DMTD, only Zn(DMTD)₂ forms. It will be apparent,that Reaction 1 is convenient in that it does not yield by-products. Inpractice, the synthesis according to reaction 1 was carried out asfollows:

1 mol (81.4 g) of high grade ZnO, of 0.25 micron average particle size,was re-slurried in 300 ml water by intense agitation and by heating to50-60° C., after which the same conditions were maintained for 1 (one)hour. Concurrently, an aqueous suspension was prepared by stirring, atambient temperature, 2 moles of DMTD (from R.T. Vanderbilt Company,Inc.) in 2000 ml water.

Reaction 1 was realized by gradually transferring, in about 30 min., theaqueous suspension of DMTD into the intensively stirred suspension ofZnO and by maintaining the same conditions, at 50-60° C., for 2 (two)hours. Subsequently, the solid phase was isolated by filtration, driedat 100-105° C. to 0.5-2% moisture content and pulverized. Notably, theprocess water was integrally recyclable.

Relevant analytical data and IR spectrum are presented below, in Table 1and FIG. 1, respectively.

TABLE 1 Measured quality parameters Determined values appearance Yellowpowder specific gravity 2.2 solubility in water, at 24° C. 0.4 g/l pH(saturated extract) 4.5-5.0 yield, g 355.0

Example 2

This example is intended to disclose one synthesis procedure applicablefor incorporating DMTD into a complex solid matrix corresponding to thegeneral composition of 45% Zn(DMTD)₂/32% Zn₃(PO₄)22H₂O/23% ZnO.

In practice, the synthesis was carried out as follows:

6.33 moles (515.0 g) of high grade ZnO (0.25 micron average particlesize), was re-slurried in 2000 ml water at 50-60° C. and intenseagitation for 1 (one) hour. After that, 1.5 moles of H₃PO₄, as 50%solution, were introduced gradually into the ZnO slurry and the sameconditions were continued for 30 minutes. Subsequently, an aqueoussuspension of 2.5 moles of DMTD in 1500 ml water was introduced in about30 minutes. The intensively stirred slurry was heated to 75-80° C. andthe same conditions were maintained for 2 (two) hours. The solid phasewas isolated by filtration, dried at 100-105° C. to 0.5-2% moisturecontent and pulverized.

Relevant analytical data are presented below, in Table 2.

TABLE 2 Measured quality parameters Determined values appearance Lightyellow powder specific gravity 2.7 solubility, at 24° C. 0.3 g/l pH(saturated extract) 5-6 oil absorption, lbs/100 lbs 33 yield, g 992

Example 3

Application of a DMTD derivative as a corrosion inhibitor pigment:

A pigment grade composite of 45% Zn(DMTD)₂/32% Zn₃ (PO₄)₂.2H₂O/23% ZnO,synthesized according to Example 2, was tested on aluminum,comparatively to a double control: commercial strontium chromate(Control A), which is the “gold” standard of the industry for corrosioninhibitor pigments and a molybdate-based product (Control B) consideredrepresentative of commercially available non-chromate corrosioninhibitor pigments. The test was performed in a typical two componentaircraft primer formulation, specifically recommended for aluminumprotection.

The description of the different versions of this formulation, the Testprimer and of the Control A and Control B primers, are presented below.

TABLE 3 Parts by Weight Components of Trade Names & Control FormulationsSuppliers of Components Test A B EPOXY BASE/PARTA Epoxy Resin Shell Epon1001 CX75 (1) 163.0 163.0 163.0 Solvents Glycol ether PM 148.0 148.0148.0 MIBK 36.7 36.7 36.7 Fillers RCL-535 TiO2 (2) 20.6 20.6 20.6Min-U-Sil 15 (3) 26.0 26.0 26.0 12-50 Talc (4) 49.3 49.3 49.0 CorrosionInhibitor Pigments Zn(DMTD)₂ in See Example 2. 78.0 — — solid matrixcomposite (See Example 2) Strontium SrCrO4-176 (5) — 107.5 — ChromateMoO₄ ⁽²⁻⁾ based Commercial (6) — — 86.0 pigment. Total part A - weight551.0 551.0 551.0 Volume, gallons 50.0 50.0 50.0 CATALYST/PART BHardener HY-815 67.1 67.1 67.1 Polyamide (7) Solvents Toluene 59.1 59.159.1 Isopropanol 218.5 218.5 21.5 Total Part B - weight 344.7 344.7344.7 Volume, Gallon 50.0 50.0 50.0 Raw material suppliers: (1) ShellChemical (2) S.C.M. Chemicals. (3) Unimin Corporation (4) Pfizer. (5)Wayne Pigment Corp. (6) The Sherwin-Williams Co. (7) Ciba-GeigyPart A (epoxy base) and Part B (catalyst) were mixed in 1:1 ratio byvolume, and inducted for 30 min. before application.

Example 4

This example demonstrates the efficiency of DMTD derivatives in organiccoatings in a corrosion inhibitor pigment.

In order to comparatively assess the corrosion inhibitor activity ofDMTD derivatives, the Test primer of Example 3 as well as Control A andControl B primer formulations were applied by wire-wound rod, onseveral, Alodine 1200 (MIL-C-5541) treated bare 2024 T-3 aluminum panels(from The Q-Panel Co.), at 0.6-0.8 mils dry film thickness, aged for 7days at room temperature, scribed and subsequently subjected to saltspray exposure (according to ASTM B-117) for 2000 hours. Notably, thescribes were applied in the typical cross form, at an approximate widthof 2 mm, and, in order to penetrate through the Alodine 1200 conversioncoating, at an appropriate depth.

By visual examination of their physical state at the end of the testperiod, the coatings' corrosion inhibitor performance, considereddirectly proportional to the tested pigment components' corrosioninhibitive activity, was qualified. The scribed area was especiallyexamined and the absence or presence of corrosion products,respectively, was interpreted as display of, or absence of, therespective corrosion inhibitor pigment's “throw power”. It will beapparent that the “throw power” is the discriminative characteristic ofeffective corrosion inhibitor pigments. Test results are summarized inTable 4.

TABLE 4 Qualification of “Throw Coating/inhibitor Performance Power”Pigment Tested Field Scribe Area Observed Test primer/Zn Intact Void ofcorrosion yes (DMTD)₂ in a solid products matrix (See Example 2) ControlA/SrCrO₄ Intact Void of corrosion yes products Control B/MoO₄ ⁽²⁻⁾Intact Filled with no based pigment corrosion products

Both Control coatings and the Test coating were found intact in thefield at the end of the test period and it was concluded that 2000 hoursof salt spray exposure was not sufficiently discriminant. Similarly toCrO₄ ⁻⁻, DMTD displayed throw power, however, by maintaining the scribearea void of corrosion products, in a passive state for the duration ofthe salt spray exposure test. In the same conditions, MoO₄ ⁻⁻ did notshow throw power. It was concluded that DMTD derivatives possesseffective corrosion inhibitor activity on aluminum and are applicable inpigment grades in organic primers intended for such.

Example 5

Applicability of DMTD in soluble forms in conversion coatings foraluminum protection.

DMTD based conversion coating was applied on several 2024 T-3 aluminum(the Test and Control) panels according to the following protocol:de-greasing, rinsing, deoxidizing (I), rinsing, deoxidizing (II),rinsing, treatment with DMTD (only of the Test panels), drying, posttreatment with Zr(IV)/K₂ZrF₆ solution, rinsing and drying. In practice,rinsing (performed in stirred water at ambient temperature for 1 minute)and all operations were carried out by immersion as follows:

The Test and Control panels were de-greased in an alkaline cleanersolution (containing 2% of each: Na₂CO₃ and Na₃PO₄) at 50° C. for 1minute, followed by rinsing at normal temperature for 1 minute.Deoxidizing was performed in two phases. Phase (I) was carried out in25% H₂SO₄ solution at 60° C. for 1 minute, followed by rinsing, andphase (II) was performed in 50% HNO₃ solution at normal temperature for30 seconds, followed by subsequent rinsing. DMTD based conversioncoating was applied (only on the Test panels) by immersion for 10minutes in saturated DMTD solution at 60° C., under agitation and,without rinsing, by subsequent drying at about 100-110° C. forapproximately 10 minutes. Both the Test and the Control panels (thelatter without DMTD coating) were post-treated by immersion, for 10minutes, in a solution containing 0.5% ZrNO₃+0.5% K₂ZrF₆, at 60° C.under agitation. The treatment was finalized by rinsing and drying theTest and Control panels at 110° C. for 10 minutes.

Example 6

In order to assess the quality of DMTD-based conversion coating on 2024T-3 aluminum, the Test panels were tested for corrosion resistance(according to ASTM B-117) and paint adhesion (tape test), in comparisonwith the Control panels, as well as with Alodine 1200 treated 2024 T-3aluminum panels, the latter being the standard of the industry. The testresults are presented below.

TABLE 6 Corrosion resistance Paint adhesion Tested panels Rating* after336 hours salt spray: by tape test: Test 8, some pitting Pass Control 0Fail Standard 8, some pitting Pass *rating is considered on the 0(extensive corrosion) to 10 (no corrosion) numeric scale.

As the presented data indicates, the DMTD-based conversion coating on2024 T-3 Aluminum, applied according to the present invention, possessesrobust resistance to corrosion and good paint adhesion, similar tochromate-based Alodine 1200 conversion coatings.

It was concluded that the DMTD derivatives are applicable as corrosioninhibitors in conversion coating technologies intended for aluminumprotection.

Example 7

Di-cyclohexyl mono-ammonium salt of trithiocyanuric acid was synthesizedaccording to the following procedure:

0.1 moles of di-cyclohexylamine (from Aldrich Chemical), dissolved in0.15 moles of H₂SO₄ solution of approximately 20%, was subsequentlyreacted by agitation with 0.1 mole of Na-trithiocyanurate (from AldrichChemical) dissolved in 100 ml water. After the pH was adjusted to6.5-7.0, the resultant slurry was filtered, washed to a soluble,salt-free condition, dried at approximately 100° C. and the solidproduct was subsequently pulverized.

Yield: 34 g, 95% of theoretical.

The relevant IR spectrum is presented in FIG. 2.

Example 8

Di-cyclohexyl mono-ammonium salt of DMTD was synthesized as follows:

0.2 moles of DMTD (from R.T. Vanderbilt Company, Inc.), previouslydissolved in 150 ml aqueous solution containing 0.28 moles of NaOH, wasreacted with 0.2 moles of dicyclohexylamine dissolved in 100 ml solutioncontaining 0.14 moles of H₂SO₄.

After the pH was adjusted to 6.5-7.0, the resultant slurry was filtered,washed to a soluble, salt-free condition, dried and subsequentlypulverized.

Yield: 66 g, approximately 90% of theoretical.

Relevant IR spectrum is presented in FIG. 3.

Example 9

Bi-DMTD (1:3) salt, or Bi(DMTD)₃, was synthesized as follows:

Initially, (A) was prepared by dissolving 0.15 moles of Bi(NO₃).5H₂O in1000 ml aqueous solution containing 0.5 moles of HNO₃, and (B) wasprepared by dissolving 0.46 moles of DMTD in 1000 ml solution containing0.92 moles of NaOH.

Bi(DMTD)₃ was subsequently obtained by introducing (A) and (B), atidentical delivery rates and simultaneously, into 200 ml water underintense agitation. After the pH was adjusted to 3.0, the obtained slurrywas stirred for 1 hour, filtered, washed to soluble salt free condition,dried at 110° C. overnight and pulverized.

Yield: 98 g, approx. 99% of theoretical.

Relevant IR spectrum is presented in FIG. 4.

Example 10

Poly-aniline/Trithiocyanuric acid (2:1) microcomposite was preparedaccording to the following procedure:

Initially, an aqueous suspension of Trithiocyanuric acid was prepared byreacting 0.05 moles of trisodium salt of trithiocyanuric acid (or2,4,6-Trimercapto-s-triazine trisodium salt) dissolved in 200 ml water,with 0.16 moles of H₂SO₄ under intense agitation. Subsequently, apreviously prepared aqueous solution, containing 0.1 mole aniline and0.22 moles of HCl in 200 ml water, was added to the above-describedsuspension. Finally, 23 g ammonium persulfate (as an aqueous solution)and 0.5 g of FeCl₃ was introduced into the reaction system, which wasstirred overnight at room temperature. The resultant dark green slurrywas filtered, washed to soluble, salt-free conditions, dried at 70-100°C. and pulverized.

Yield: 17 g

Relevant IR spectrum is presented in FIG. 5.

Example 11

Zn(II) salt of trithiocyanuric acid, ZnTMT 1:1, was produced accordingto the following procedure:

Solution (A), containing 0.1 mole of trisodium salt of trithyocyanuricacid in 500 ml water, and solution (B), containing 0.1 mole of Zn(NO₃)₂and 0.1 mole of HNO₃ in 500 ml water, were introduced simultaneously andat identical delivery rates, into 200 ml of intensively stirred water atabout 50° C. The pH of the obtained slurry was adjusted to about 5 andafter 1 (one) hour, during which the reaction conditions were maintainedthe same, the solid phase was separated by filtration, washed to solublesalt-free conditions, dried at 110° C. overnight and subsequentlypulverized.

Yield: 22 g, 89% of theoretical.

Pertinent IR spectrum is presented in FIG. 6.

While the invention may be used in connection with a paint, it may alsobe used in connection with other protective coatings. For example,sol-gel protective coatings, which are generally known in the art, aresilane-based, applicable for aluminum protection, and are considered asreplacement of chromate-based conversion coatings such as Alodine 1200.The following example shows a practical procedure for applying thecurrent invention in connection with a typical sol-gel process.

Example 12

Several Al 2024 T-3 Aluminum panels were degreased, and also de-oxidizedin identical fashion as described in Example 5, and subsequentlyair-dried.

Solution (A) was prepared by dissolving 0.02 moles of diethylenetriamineand 0.01 moles of DMTD, in 100 ml water.

Solution (B) was prepared by the addition of 0.02 moles oftetramethoxysilane and 0.06 moles of glycidoxypropyltrimethoxysilaneinto 200 ml water and by adjusting the pH of the solution to about 4-4.5with acetic acid, under continuous stirring at normal temperature.

After approximately 1 (one) hour, during which the hydrolysis process ofthe silane precursors proceeded in Solution (B), solution (A) wasintroduced into it under continuous agitation.

Test panels were prepared by the application, after about 10 minutes ofstirring, of the resulted emulsion of silane condensate onto abovespecified aluminum panels at a spread rate of approximately 0.2-0.3 mlper 100 cm² and air-dried.

Control panels were prepared in similar fashion, except that Solution(A) was void of DMTD.

Example 13

Pigment grade Sr-doped amorphous silica of SrSiO₃.11SiO₂.5.7H₂Ocomposition, containing approximately 9.5% Sr species, was synthesizedaccording to the following procedure:

Initially, solution A was prepared by reacting 0.51 mole of SrCO₃ and3.5 moles of HNO₃ and adjusting the volume of the resulted solution to1300 ml with water. Solution B was prepared by dissolving 1.9 moles ofsodium silicate of Na₂O (SiO₂)_(3.22) composition (from Hydrite ChemicalCo., WI), in 900 ml of water.

Solutions A and B were delivered simultaneously and with identical ratesfor approximately 1 (one) hour into 500 ml of intensively stirred waterat 70-85° C. At the end, the pH was adjusted to 8-8.5 and the sameconditions were maintained for an additional 2 (two) hours, after whichthe resultant solid phase was separated by filtration, washed tosoluble, salt-free conditions, dried at approximately 105° C. overnight,and pulverized.

Relevant analytical data and IR spectrum results are presented below inTable 13 and FIG. 7, respectively.

TABLE 13 Measured Parameters Determined Values appearance White powderspecific gravity 1.8-1.9 pH(saturated extract) 9.0-9.3 oil absorption,lbs/100 lbs 52-60 Sr, % (calculated) 9.5 H₂O, % (by ignition at 600° C.)16.5 yield, g 471

Example 14

A pigment grade mixture of trithiocyanuric acid and Sr-doped AmorphousSilica of SrSiO₃.11SiO₂.5H₂O+1TMT (approximate composition), containingabout 8% Sr (calculated) and 17% TMT (calculated), was produced asfollows:

100 g of trithiocyanuric acid, in powder form, was blended into 460 g ofSr-doped amorphous silica in dry granular form. The Sr-doped amorphoussilica was synthesized and processed as shown in Example 13. Theobtained mixture was subsequently pulverized to a fineness of about 6 onthe Hegman scale.

Trithiocyanuric acid was obtained from an aqueous solution oftri-sodium-trithiocyanurate, by adjusting the solutions pH to about 3,filtering, washing, and drying the resultant solid phase.

Relevant analytical data and IR spectrum results are presented below inTable 14 and in FIG. 8, respectively.

TABLE 14 Measured Parameters Determined Values appearance Light yellowpowder specific gravity 1.7 pH(saturated extract) 6.9 oil absorption,lbs/100 lbs 75-85 Sr, % (calculated) 7.9 TMT % (calculated) 17 Yield, g560

Example 15

This example is intended to demonstrate the application oftrithiocyanuric acid (“TMT”) as a corrosion inhibitor constituent of anamorphous silica+TMT pigment grade mixture in a typical coil coatingformulation.

The pigment grade mixture of SrSiO₃.11SiO₂.5H₂O+1TMT composition wassynthesized according to the process in Example 14, and was tested (SeeTest formulation, Table 15) on galvanized steel (from L.T.V. Steel Co.),in comparison with commercial Strontium chromate (Control A formulation,Table 15), the “gold” standard of the industry for corrosion inhibitorpigments, and respectively, Sr-doped amorphous silica synthesizedaccording to Example 13 (Control B formulation, Table 15).

The typical solvent-borne polyester coil primer formulation isspecifically recommended for galvanized steel protection. Description ofthe test formulation, and control formulations A and B are presentedbelow in Table 15.

TABLE 15 Parts by Weight Trade Names & Control Components of Suppliersof Test Formulation Formulations Components Formulation A B PolyesterResin EPS 3302 (1) 536.0 536.0 536.0 Solvents Aromatic 150 118.0 118.0118.0 Diacetone 73.5 73.5 73.5 Alcohol Fillers RCL-535 TiO₂ (2) 46.046.0 46.0 Aerosil R.972 (3) 2.1 2.1 2.1 Catalyst Cycat 4040 (4) 7.6 7.67.6 Hardener Cymel 303 (4) 73.6 73.6 73.6 Corrosion Inhibitor PigmentsStrontium SrCrO₄-176 (5) — 143.5 — Chromate Sr-doped As shown in — —120.0 amorphous Example 13 silica Sr-doped silica + As shown in 150.0 —— TMT pigment Example 14 grade mixture Total Weight 1006.8 1000.3 976.8Raw Material Suppliers: (1) Engineering Polymer Solutions (2) MillenniumInorganic Materials (3) DeGussa Corporation (4) Cytec. (5) Wayne PigmentCorporation

The formulation was ground to a fineness of 6.5-7.0 Hegman beforeapplication.

Example 16

This example demonstrates the applicability of di-mercapto and tri-thioderivatives according to the present invention, as corrosion inhibitoradditives in paint formulations. Specifically, the application oftrithiocyanuric acid—di-cyclohexylamine salt of a 1:1 ratio, as anadditive in a typical coil primer formulation, is disclosed.

The coil primer formulation prepared was identical to the testformulation described in Example 15 (See Table 15), except that thecorrosion inhibitor constituent consisted of 120 parts by weightSr-doped Amorphous Silica, prepared according to example 13, and 30parts by weight of trithiocyanuric acid-di-cyclohexylamine salt of a 1:1ratio. This was introduced into the formulation to end up with 1006.8parts by weight of paint and ground to 6.5-7.0 fineness on the Hegmanscale. The trithiocyanuric acid-di-cyclohexylamine 1:1 salt wassynthesized according to Example 7 of the present invention.

Consequently, the corrosion inhibitor constituent of the testformulation according to Example 16 consists of an ordinary physicalmixture of the above two components. The results are shown in Table 17(See Example 17).

Example 17

This Example demonstrates the efficiency of di-mercapto derivatives, ingeneral, and of trithiocyanuric acid and its derivatives, in particular,as corrosion inhibitor pigments or additives in coil primer formulationsand on typical coil substrates, such as galvanized steel. It will be,however, apparent to one skilled in the art that the concept of thepresent invention applies for primers intended for steel protection ingeneral.

In order to comparatively assess the corrosion inhibitor activity oftrithiocyanuric acid and its derivatives, the test primers of Examples15 & 16, along with control formulations A & B from Example 15, wereapplied by wire-wound rod, on several galvanized steel panels (fromL.T.V. Steel Co.), at 0.6-0.7 mil dry film thickness, aged for at least2 (two) days at room temperature, scribed and subsequently subjected tosalt spray exposure (according to ASTM B-117).

The scribes were applied in the typical cross form, and, in order to cutthrough the protective galvanic zinc coating from the area of thescribes, at appropriate depth. During salt spray exposure, the coatings'physical state was assessed periodically by visual examination. Scribeareas were observed for the absence or presence of corrosion products(white rust), and “field” areas were observed for the physical integrityof coatings and the presence of white rust.

Notably, the protective performance of the tested coatings was qualifiedby the service life of coatings, defined as the total hours of saltspray exposure that result in extensive corrosion along the scribes andconsiderable corrosion in the “field” areas. Service life of a coatingis considered directly proportional to the related pigments' oradditives' corrosion inhibitor performance, which is convenientlyqualified by E_(i), the Inhibitor Efficiency Index, defined as:E_(i)=100[(service life)_(TEST)−(service life)_(CONTROL)]/(servicelife)_(CONTROL).

It is important to note that the service life of control formulation Afrom Example 15, containing SrCrO₄ as a corrosion inhibitor pigment, wasconsidered as the test control, or (service life)_(CONTROL).

It will be apparent, that values of E_(i)>0 indicate comparativelybetter corrosion inhibitor performance than the control's (SrCrO₄'s)performance, whereas values of E_(i)<0 indicate a poorer corrosioninhibitor performance than that of the control. The test results aresummarized below in table 17.

TABLE 17 Inhibitor Pigment or Service life of Test additive/coatingCoating (hours) E_(i) % 1. Trithiocyanuric acid-di-cyclohexykamine, 300087 1:1 salt and Sr-doped amorphous silica mixture, as described by thetest primer in table 16 (Ex. 16). 2. Trithiocyanuric acid + Sr- doped2000 25 amorphous silica pigment grade mixture, as described by the testprimer in table 15 (Ex. 15). 3. SrCrO₄, as described by control A intable 1600 0 15 (Ex. 15) 4. Sr-doped amorphous silica, as 1000 −37described by control A in table 15 (Ex. 15).

The disclosed E_(i) values indicate that, in comparison with Sr-dopedamorphous silica, trithiocyanuric acid and trithiocyanuricacid-di-cyclohexylamine, 1:1 salt significantly extend the service lifeof the coatings. Trithiocyanuric acid extends the service life of coilcoatings on galvanized steel by 100% over Sr-doped amorphous silica, andtrithiocyanuric acid -di-cyclohexylamine, 1:1 salt, extends the servicelife by 200% over Sr-doped amorphous silica. Likewise, both compoundsdisplay better corrosion inhibitor performance than SrCrO₄, and morespecifically trithiocyanuric acid -di-cyclohexylamine 1:1 salt. Also,Sr-doped amorphous silica, as expected, displayed significantly poorerinhibitor performance than SrCrO₄.

With no intent to limit the concept of the present invention, Examples18-21 delineate procedures for synthesizing conductive polymers dopedwith DMTD and some of its derivatives. More specifically, in thefollowing examples, procedures for synthesizing salts of polyanilineformed with as DMTD and (DMTD)₂ are presented.

Example 18

An inherently conductive polyaniline-phosphoric acid salt (symbolized by(PANI)-(H₃PO₄) generic formula) which will form the basis for Examples19 and 20, was synthesized according to the following procedure:

In an open beaker 9.4 g (0.1 moles) of aniline was added to 600 mL ofintensively stirred cold water containing 8.5 g (0.086 moles) of H₃PO₄.Subsequently, 20 g of ammonium persulfate (as an aqueous solution ofapproximately 20% (NH₄)₂S₂O₈)) was added into the system and theconditions were maintained for three (3) hours. The polymerizationprocess resulted in an aqueous suspension of a finely divided dark greenpolyaniline salt. The salt also formed a thin coating on the equipmentin contact with the reaction medium, which will cause a reduction in themeasured yield.

The dispersed phase was separated by filtration, washed to a saltcontaminant-free condition, subsequently dried at approximately 70° C.overnight, and pulverized. The characteristics of the conductive polymerwere recorded, as shown in Table 18 and FIG. 9.

In order to assess its conductivity, a small sample of the polyanilinewas pelletized at 2000 psi. When measured at two contact points, thepolyaniline was found conductive as shown in Table 18 (see bulkconductivity).

TABLE 18 Appearance Dark green powder Bulk Conductivity, (siemens/cm)~1.6 × 10⁻⁴ Specific Gravity 1.5 pH, in saturated leachet 2.2 Yield 7.6g

Example 19

Without being separated, the suspended conductive polyaniline salt fromExample 18 was de-protonated by adjusting the pH of the aqueous phase tobetween 9 and 10 and maintaining the same pH under agitation for two (2)hours. The pH was adjusted by adding either diluted NH₄OH or dilutedNaOH. The resultant polyaniline base (emeraldine base, symbolized by(PANI) generic formula) was dark blue in color and it was found to benon-conductive following the procedure described in Example 18.

Subsequently, the dispersed polyaniline base was separated byfiltration, washed with water to a soluble salt contaminant-freecondition, and re-dispersed into 200 mL water by intense agitation. ThepH of the resultant suspension was measured at 7.7.

Relevant IR spectrum is presented in FIG. 10.

Example 20

The polyaniline base from Example 19 was used to produce a DMTD salt ofpolyaniline symbolized by (PANI)-(DMTD) generic formula. It was producedby re-protonating the polyaniline base with DMTD according to thefollowing procedure:

10.0 g (0.06 moles) of purified and finely ground DMTD, in 300 mL water,was added into the polyaniline base suspension from Example 19. There-protonation process was completed by extensively stirring thesuspension for twelve (12) hours at 40-50° C. At that time, the pH ofthe aqueous phase was measured to be 3.2.

The dispersed phase was separated by filtration, washed to a solublecontaminant-free condition, subsequently dried at approximately 70° C.overnight, pulverized, and then the characteristics of the conductivepolymer were recorded, as shown in Table 20. Relevant IR spectrum ispresented in FIG. 11.

TABLE 20 Appearance Dark green powder Bulk Conductivity, siemens/cm 1.6× 10⁻³ Specific Gravity 1.7 pH, in saturated leachet 2.3 Yield 17.8 g

Example 21

A polyaniline-(DMTD)₂ salt, symbolized by (PANI)-(DMTD)₂ genericformula, was synthesized according to the following procedure.

In an open beaker, 9.4 g (0.1 moles) of aniline (99% purity) was addedto 600 mL intensively stirred cold water. Following this, 9.5 g (0.03moles) of (DMTD)₂ was gradually introduced into the beaker.Subsequently, 20 g of ammonium persulfate (as an aqueous solution ofapproximately 20% (NH₄)₂S₂O₈)) was added into the system, and the sameconditions were maintained for six (6) hours. The polymerization processresulted in an aqueous suspension of finely divided dark green solid andthe pH of the aqueous phase was measured at 2.4.

The resultant polyaniline-(DMTD)₂ salt was separated by filtration,washed with water to a soluble contaminant-free condition, driedovernight at approximately 70° C. then pulverized, and its propertieswere recorded. The results may be seen below in Table 21 and therelevant IR spectrum may be seen in FIG. 12.

TABLE 21 Appearance Dark green powder Bulk conductivity, siemens/cm 3.3× 10⁻⁵ Specific Gravity 1.85 pH, in saturated leachet 2.5 Yield 14.7 g

Example 22

With no intent to limit the concept of the present invention, thisexample discloses a synthesis process where DMTD is integrated into acomplex inorganic matrix comprising additional corrosion inhibitorspecies, and specifically Ce(III), Zn(II) and molybdate species. It willbe apparent to one skilled in the art that the specific composition ofthe complex inorganic matrix can be varied as a function of the chemicalidentity of precursors, as well as a function of the chosenstoichiometrical ratios.

A pigment grade corrosion inhibitor of

Ce₂(MoO₄)₃/Ce₂(CO₃)₃/1.46 Zn(DMTD)₂ generic composition was synthesizedin a “one step” process involving the anticipated reactions, based uponthe products' solubilities, as follow:0.22ZnO+0.31Ce₂(CO₃)₃+0.47MoO₃.H₂O+0.44DMTD→0.15Ce₂(MoO₄)₃+0.22Zn(DMTD)₂+0.16Ce₂(CO₃)₃+0.45CO₂+0.67H₂O

In practice, the synthesis was carried out as disclosed below:

A mixed dispersion, consisting of 145 g (0.31 moles) of finely groundtechnical grade Ce₂(CO₃)₃ and 18 g (0.22 moles) of high quality ZnO in600 ml water, was prepared by intense stirring for one hour at ambienttemperature. Concurrently, a distinct mixed dispersion, containing 68 g(0.47 moles) of finely ground MoO₃ and 66 g (0.44 moles) of DMTD in 500ml water, was also prepared in identical fashion.

After combining the two dispersions, the reaction mixture was heated to60-65° C. under intense stirring. The synthesis process was finalized bymaintaining the same conditions for about 12 hours. Subsequently, theresulted solid phase was separated by filtration, dried at 70° C.overnight, pulverized and characterized.

Quality parameter values and relevant IR spectrum are presented in Table22 and FIG. 13, respectively.

TABLE 22 Appearance yellow powder specific gravity 3.34 pH, in saturatedleachate 4.9 Oil absorption, lb/100 lb 36 Zn(DMTD)₂, % (calculated) ~29Yield, g 266The yield and the IR spectrum essentially confirm the anticipatedgeneric composition specified above.

What is claimed is:
 1. A process for protecting an aluminum substrate ora steel substrate against corrosion comprising: providing an aluminumsurface to be protected, applying to said surface a protectivecomposition comprising of a pigment grade corrosion inhibitorcomposition, said protective composition being formed by reacting anorganic compound from a group consisting of di-mercapto andpoly-mercapto derivatives and their derivatives, with a cationic speciesselected from a group consisting of Bi(III), Co(II), Cd(II), Ag(I),Sb(III), Ni(II), Li(I), La(III), and Pr(III), said protective pigmentgrade corrosion inhibitor composition having a limited solubility inwater of between about 0.01 and about 1000 mmoles/per liter of water,whereby said pigment grade corrosion inhibitor composition is capable ofpreventing corrosion for at least 2000 hours in salt spray exposureconditions.
 2. A process according to claim 1 wherein said protectivecomposition is applied as a layer of less than approximately 20 micronsin thickness.
 3. A process according to claim 1 wherein said protectivecomposition has a limited solubility in water of between about 0.1 andabout 10 mmoles/ liter.
 4. A process according to claim 1 wherein saidprotective composition is applied as an aqueous solution and issubsequently dried whereby a conversion coating is formed on saidsubstrate, said conversion coating being subsequently coated with apaint.
 5. A process according to claim 1 wherein said protectivecomposition is incorporated into a silane-based gel coating.
 6. Aprocess according to claim 1 wherein said protective corrosion inhibitorcomposition is selected from the group consisting of2,5-dimercapro-1,3,4 thiadiazole or (DMTD),2,4-dimercapto-s-triazolo-[4,3-b]-1,3-4-thiadiazole, trithiocyanuricacid or (TMT), derivatives of DMTD, and derivatives of TMT,dithiocyanuric acid, dimercaptopyridine, 2,4-dithiohydantoine, and2,4-dimercapto-6-amino-5-triazine.
 7. A process according to claim 1wherein said protective composition pigment grade corrosion inhibitorcomposition is selected from the group consisting of M(DMTD)_(n) wheren=1,2 or 3, and M is a metal cation selected from the group consistingof Bi, Co, Ni, Cd, Ag, Sb, Li, La, Pr; alkyl ammonium salts of DMTD and(DMTD)_(n); cyclo-alkyl ammonium salts of DMTD and (DMTD)_(n); di-cycloalkyl ammonium salts of DMTD and (DMTD)_(n); aryl ammonium salts ofDMTD; aryl ammonium salts of (DMTD)_(n); quaternary ammonium salts ofDMTD; quaternary ammonium salts of (DMTD)_(n); polyaniline,polythiophen, and polypyrrol doped with DMTD; polyaniline, polythiophen,and polypyrrol doped with (DMTD)₂; and micro and nano composites of polyDMTD/polyaniline, DMTD/polythiophen and poly DMTD/polypyrrol.
 8. Aprocess according to claim 1 wherein said protective composition isapplied by incorporating the same in a curable polymeric coatingcomposition and applying said composition over said substrate.
 9. Aprocess according to claim 1 wherein said protective composition pigmentgrade corrosion inhibitor composition is selected from the groupconsisting of: N- or S- and N-, N-, S- and N-, S-substituted derivativesof DMTD such as, 5-mercapto-3-phenyl-1,3,4-thiadiazoline-2-thione(Bismuthiol II), substituted derivatives of 5,5′ dithio-bis(1,3,4thiadiazole-2(3H)-thione (DMTD)₂, substituted derivatives of5,5′-Thiobis (1,3,4-thiadiazole-2(3H)-thione substituted derivatives ofdimercaptopyridine, and of 2,4-dithiohydantoine, substituted derivativesof 2,4-dimercapto-6-amino-5-triazine and (DMTD)_(n), a polymer of DMTD;a salt of DMTD of general formula, M(DMTD)_(n), where n=1,2 or 3, and Mis a metal cation and M=Bi, Co, Ni, Cd, Ag, Sb, Li, La, Pr; a salt of(DMTD)_(n) of general formula M[(DMTD)_(n)]_(m), where n=2 or n>2,m=1,2, or 3 and M=Bi, Co, Ni, Cd, Ag, Sb, Li, La, Pr; alkyl ammoniumsalts of DMTD and (DMTD)_(n); cyclo-alkyl ammonium salts of DMTD and(DMTD)_(n); di-cyclo alkyl ammonium salts of DMTD and (DMTD)_(n); arylammonium salts of DMTD and (DMTD)_(n); quaternary ammonium salts of DMTDand (DMTD)_(n); polyammonium salts of DMTD and (DMTD)_(n) formed with apolyamine; polyaniline, polypyrrole and polythiophen doped with DMTD;polyaniline, polypyrrole and polythiophen doped with (DMTD)₂; micro andnano composites of poly DMTD/polyaniline, poly DMTD/polypyrrole, andpoly DMTD/polythiophen; DMTD, salts of DMTD, and derivatives of DMTD, asconstituents of an inorganic matrix; and a combination of said forms.10. A process according to claim 1 wherein said protective compositionpigment grade corrosion inhibitor composition is selected from the groupconsisting of: S-substituted derivatives of trithiocyanuric acid (TMT);a salt of TMT of general formula, M(TMT)_(n), where n=1,2 or 3, and M isa metal cation and M=Bi, Go, Ni, Cd, Ag, Sb, Li, La, Pr; alkyl ammoniumsalts of TMT; cyclo-alkyl ammonium salts of TMT; dicyclo alkyl ammoniumsalts of TMT; aryl ammonium salts of TMT; quaternary ammonium salts ofTMT; polyamines formed with TMT; polyaniline doped with TMT; polypyrroleand polythiophen doped with TMT; micro and nano composites of polyTMT/polyaniline, poly TMT/ polypyrrole, and poly TMT/polythiophen; TMT,salts of TMT; and derivatives of TMT, as constituents of an inorganicmatrix; salts of TMT and derivatives of TMT in encapsulated form in apolymer matrix, or as a cyclodextrin-inclusion compound; and acombination of said forms.
 11. The protective composition of claim 1wherein the protective composition is used in a paint.
 12. A process forproducing a pigment grade corrosion inhibitor composition comprising thesteps of: providing a first aqueous slurry containing zinc oxide (ZnO);providing an aqueous suspension containing 2,5-dimercapto-1,3,4thiadiazole or (DMTD); and transferring said aqueous suspension to saidaqueous slurry; wherein the ZnO and DMTD are added in a 1:2stoichiometrical relationship of ZnO and DMTD.
 13. The process accordingto claim 12 further comprising the steps of: separating the solid phaseout of the resulting slurry; and drying the solid phase.